Down-hole air hammer

ABSTRACT

A down-hole air hammer embodying an outer housing structure connectible to a string of rotatable drill pipe through which compressed air is conducted. Upper and lower cylinder sleeves within the housing structure define an upper high pressure air annulus and a lower low or exhaust pressure annulus, the cylinder sleeves being longitudinally spaced from each other. A hammer piston reciprocates in the sleeves, having an enlarged intermediate portion slidable along the housing structure between the cylinder sleeves, there being small diameter upper and lower pistons slidable along the upper and lower cylinder sleeves, respectively, to provide a large intermediate piston area over which high pressure air can act to increase the impact force of the piston on a companion anvil secured to the drill bit rotatable by the housing structure. The high pressure air exhausts through the housing structure above the bit to provide sufficient air volume for carrying the cuttings upwardly through the annulus surrounding the drill pipe to the top of the hole being drilled.

Elnited States Patent Curington 1 Jan. 23, 1973 DOWN-HOLE AIR HAMMER [75] Inventor: Allred R. Curington, Houston, Tex. [57] ABSTRACT [73] Assignee: Baker Oil Tools, Inc., City of Com- A down'hoie hammer an outer h f meme Calif structure connectible to a string of rotatable drill plpe through which compressed air is conducted. Upper [22] Filed: Dec. 23, 1970 and lower cylinder sleeves within the housing structure define an upper high pressure air annulus and a [21] Appl. No.. 100,848

lower low or exhaust pressure annulus, the cylinder sleeves being longitudinally spaced from each other. A [52] U.S. Cl ..l73/78, 173/137 hammer piston reciprocates in the sleeves, having an [5 Int. Cl. enlarged intermediate portion lidable along the housof Search i tructure between thg ylinder leeves there being small diameter upper and lower pistons slidable along References Clad the upper and lower cylinder sleeves, respectively, to UNITED STATES PATENTS provide a large mtermediate piston area over WhlCh high pressure air can act to Increase the impact force 3,480,088 11/1969 Ghelfi ..l73/l38 of the piston on a companion anvil secured to the drill 2,396,627 /19 w lm yer- .....l73/l36 bit rotatable by the housing structure. The high pres- 3,l67,136 1/1965 Cook ..l73/l36 sure air exhausts through the housing structure above $130,434 4/1965 vmcem "173/78 the bit to provide sufficient air volume for carrying the cuttings upwardly through the annulus surrounding the drill pipe to the top of the hole being drilled.

17 Claims, 8 Drawing Figures DOWN-HOLE MR HAMMER The present invention relates to drill bit apparatus for drilling a hole in a formation, and more particularly to pneumatically operated bottom hole drilling apparatus that imparts a percussive action to a drill bit, during the time the bit is preferably rotated.

Percussive types of drilling apparatus are known for lowering in a well bore for the purpose of drilling the hole as a result of a hammering action imposed upon a suitable bit connected to the apparatus. An improved type of drilling apparatus is illustrated in United States patent application Ser. No. 863,988, filed Oct. 6, 1969, for Down-Hole Drilling Hammer. In drilling small diameter holes, the down-hole drilling apparatus itself must be of correspondingly small external diameter. The piston area available in such small diameter apparatus has been limited to the point that it is difficult for the apparatus to perform effectively, particularly when only relatively low air pressures are available.

Moreover, the air for effecting reciprocation of the hammer piston that impacts upon an anvil secured to the drill bit is required to pursue a circuitous path in exhausting from the apparatus, for the purpose of carrying the cuttings upwardly through the annulus surrounding the drill pipe string to which the apparatus is secured. Regardless of the path followed, the air available for each cycle of operation of the hammer piston is of restricted volume because of the relatively small area of the piston on which the compressed air acts.

By virtue of the present invention, a down hole air hammer apparatus is provided in which the piston area on which the compressed air acts is of a much greater diameter than was heretofore available, thereby correspondingly increasing the force delivered by the piston against the anvil on its power stroke. Such increase in piston area is provided without increasing the outside diameter of the apparatus itself. Accordingly, a larger piston area is available in comparatively small diameter sizes of apparatus, making such apparatus perform more effectively, particularly under conditions in which only relatively low air pressure is available.

The apparatus also has a relatively large volume air chamber at its upper end, which permits the introduction of more high pressure air imposed on the hammer piston for its downstroke, thereby enabling more power to be developed. The use of a large diameter expansion chamber also provides more air to be exhausted from the apparatus, thereby insuring sufficient air volume to carry the cuttings upwardly out of the bore hole being drilled. In addition, a comparatively large quantity of air is exhausted directly into the bore hole annulus surrounding the apparatus, and without the necessity for passing through the anvil and out the drill bit, which avoids the necessity for the air to traverse a tortuous path before venting through the'bit. Since the air can escape more readily on the downstroke of the hammer piston, a lesser quantity of air is trapped in the air chamber on the upstroke, resulting in the reduction in the air pressure trapped in the chamber on the upstroke of the hammer piston.

In general, the intermediate or center portion of the hammer piston is enlarged to slidably seal against the outer housing or cylinder of the apparatus, the upper and lower portions of the hammer piston being of smaller diameter and controlling the flow of air to opposite ends of the hammer piston in effecting its reciprocation. The power air exerted on the piston on its downstroke acts on the enlarged intermediate portion of the piston to cause the piston to impact on the anvil of the apparatus therebelow with a much greater force. The power air also exhausts directly through the enlarged outer housing into the annulus surrounding the apparatus, permitting its ready escape and minimizing the amount of air trapped above the piston on its upstroke, as noted above.

This invention possesses many other advantages, and has other purposes which may be made more clearly apparent from a consideration of a form in which it may be embodied. This form is shown in the drawings accompanying and forming part of the present specification. It will now be described in detail, for the purpose of illustrating the general principles of the invention; but is is to be understood that such detailed description is not to be taken in a limiting sense.

Referring to the drawings:

FIGS. 1a, lb and 1c together constitute a longitudinal section through an apparatus embodying the invention, with parts in their relative position after the hammer piston has completed delivering an impact blow against its companion anvil and the drill bit securedthereto, FIGS. 1b and la being lower continuations of FIGS. and 1b, respectively;

FIGS. 2a and 2b are views similar to FIGS. la-lc, with the hammer piston in its upper position, FIG. 2b being a lower continuation of FIG. 20;

FIG. 3 is an enlarged cross-section taken along the line 33 on FIG. 1c;

FIG. 4 is an enlarged partial cross-section taken along the line 44 on FIG. 10;

FIG. 5 is an enlarged cross-section taken along the line 5-5 on FIG. lb.

The down-hole drilling hammer A illustrated in the drawings is connected to the lower end of a string of drill pipe B extending to a drilling rig (not shown) at the top of a bore hole C being drilled, and by means of which the apparatus and a drill bit D at its lower end are rotated while compressed air, or other suitable fluid medium, is pumped down the drill pipe for operating the apparatus. The drill bit D is of any suitable type and may have sintered tungsten carbide inserts (not shown) mounted in its end face for impacting against the bottom F of the bore hole while the apparatus A and bit D are being rotated, to impart a drilling action against the full area of the bottom of the hole as a result of the impacting action imparted to an anvil l0 disclosed as integral with the drill bit, although the drill bit may be connected to the anvil in any other suitable manner.

The drilling hammer apparatus A includes an outer elongate housing structure 11 made of several sections or components, including an upper section 12 threadedly secured to an upper sub 13 having an upper threaded box 14 for attachment to the lower pin 15 of an adjacent drill pipe section B. The lower end of'the upper section 12 is threadedly secured to an intermediate coupling section 1 6 which is, in turn, threadedly attached to a lower housing section 17, the lower end of which is threadedly secured to a lower sub 18 integral with a lower cylinder sleeve 19 extending upwardly therefrom and spaced laterally from the housing to form an annular exhaust passage 20 therewith. Upper radial exhaust ports 21 extend through the upper portion of the cylinder sleeve, establishing communication between the interior of the sleeve and the exhaust passage whereas, lower generally radial exhaust ports 22 extend through the sleeve, establishing communication between the exhaust passage 20 and the interior of the sleeve 19. The upper portion of the lower sleeve carries a suitable side seal ring 23 thereon sealing against the inner wall 24 of the lower housing section 17 immediately above the annular exhaust passage 20.

An upper cylinder sleeve 25 is integral with an extends downwardly from the intermediate coupling section 16 within the lower housing section 17, being laterally spaced therefrom to provide a high pressure annular air passage 26 therebetween. The lower end of this sleeve 25 carries a suitable side seal ring 27 sealing against the wall 24 of the lower housing section, the cylinder sleeve having a plurality of lower radial inlet ports 28 establishing communication between the high pressure air passage 26 and the interior of the upper sleeve, and also having upper ports 29 establishing communication between the upper end of the annular passage 26 and the lower end of an annular inlet passage 30 formed between an inner tubular member or sleeve 31 having a head 32 engaging the inner wall 33 of the upper sleeve below its ports 29, and sealed thereagainst by a suitable elastomer head seal 34 also engaging the wall of the sleeve 25. The tubular member 31 is elongate, extending upwardly through the coupling 16 and to the upper portion of the upper housing section 12, encompassing a lower head 35 of the upper sub 13, against which it is sealed by a suitable elastomer side seal member 36 on the head engaging the wall 37 of the inner tubular member 31.

Compressed air pumped downwardly through the tubular string B can enter a central passage 38 through the upper sub, which communicates with side ports 39 in the sub opening into the upper end of the annular inlet passage 30, such air being capable of passing through the upper ports 29 in the upper cylinder sleeve 25 into the high pressure passage 26, and then through the inlet ports 28 at the lower portion of the sleeve 25.

It is to be noted that the upper and lower cylinder sleeves 25, 19 are longitudinally spaced from one another to a substantial extent, allowing a cylinder portion 40 of the lower housing section to be provided therebetween of a substantially greater inside diameter than the inside diameters of the upper and lower cylinder sleeves, discharge or exhaust ports 41a extending through the larger diameter cylinder 40 and establishing communication between its interior and the exterior of the housing 1 l.

A hammer piston 41 is reciprocable within the upper and lower cylinders 25, 19 and the intermediate, larger diameter cylinder member 40 therebetween. This piston includes an upper piston portion 42 slidable longitudinally in the upper cylinder sleeve 25, a lower piston portion 43 slidable longitudinally in the lower cylinder sleeve 19, and an enlarged intermediate piston portion 44 integral with such upper and lower piston portions and slidable along the inner wall 24 of the enlarged cylinder. The piston 41 is adapted to be shifted downwardly to deliver an impact blow against the upper impact head 45 of the anvil 10 mounted within the lower cylinder sleeve 19 and lower sub 18, this anvil being integral with the drill bit D, or other wise suitably secured thereto. The anvil makes a spline connection with the lower sub 18, to permit longitudinal movement of the anvil and bit with respect to the lower sub 18, and also to enable the rotary motion of the drill pipe 13 to be transmitted through the upper sub 13 and housing 1 l to the lower housing sub 18, and then to the anvil l0 and drill bit D. As specifically shown, the anvil connection is provided by inwardly extending circumferentially spaced splines 46 on the lower sub slidably meshing with companion splines 47 on the anvil.

When the drill bit D engages the bottom F of the hole and the housing 11 and its lower sub 18 are disposed in a downward position with respect to the anvil and bit,

as determined by engagement of the lower end 18a of the lower sub with an upwardly facing shoulder 10a on the anvil, the impact head 45 is disposed within the lower cylinder sleeve 19 above its ports 22, making a close fit therewith. At this time, when the piston 41 has been disposed in its uppermost position within the housing and sleeves 25, 19 (FIGS. 2a, 2b), compressed air can exhaust through the upper ports 21 into the exhaust annulus 20, and then through the lower ports 22 to the interior of the sleeve 19, such air continuing to flow through inlet ports 50 in the upper portion of the anvil into its central passage 51, discharging through lower nozzles or passages 52 in the drill bit against the bottom F of the bore hole C to clean the bottom of cuttings, clean the bit D, and convey such cuttings around the drill bit and upwardly through the annulus surrounding the housing 11, and the annulus surrounding the drill pipe B to the top of the bore hole. The upper end of the central passage 51 is closed by a suitable plug 53.

The lower piston portion 43 has suitable seal means on its periphery for sealing against the inner wall of the lower cylinder sleeve. As illustrated, such seal means may take the form of a labyrinth seal provided by a series of circumferential external grooves 54 in the piston in which air will be trapped. When the piston is in its lowermost position against the impact head, the seals 54 extend from a location above the lower exhaust ports 22 to a location above the upper exhaust ports 21. The piston has a longitudinal hammer return passage 55 extending therewithin from its lower end and into communication with an upper annular inlet groove 56,

which will be in registry with the inlet ports 28 when the hammer piston is in its lowermost position (FIGS.-

la-lc). The piston also has a longitudinal impact passage 57 in its upper small diameter portion extending from the upper end of the piston and communicating with an elongate lower side port 58 which opens into the annular space 59 between the small diameter piston 42 and the enlarged cylinder 40 when the piston is in its lower position. The small diameter upper piston portion 42 has suitable seal means 60 thereon on opposite sides of its inlet groove 56 which can assume any desirable form. As shown, labyrinth seal grooves 60 are provided capable of trapping air and sealing against the inner wall of the upper cylinder sleeve 25.

The enlarged intermediate piston portion 44 slidably seals against the wall 24 of the enlarged cylinder 40; This intermediate piston portion carries an upper seal ring 61, such as a piston ring, therein near its upper portion and a lower piston ring 62 at its lower portion, so as to prevent leakage along the enlarged hammer piston portion 44.

When the hammer piston 41 is in its lowermost position, as illustrated in FIGS. lb and 1c, the lower piston portion 43 closes the upper exhaust ports 21, but its upper annular groove 56 is aligned with the inlet ports 28, its labyrinth seals 60 being disposed on opposite sides of the latter. The enlarged piston portion 44 seals against the enlarged cylinder 40 below the discharge ports 41a. When the piston is in the position illustrated in FIGS. lb and 1c, air in the cylinder space or chamber '65 within the upper tubular member 31 and in the upper cylinder sleeve 25 above the piston will have exhausted through the impact passage 57 and its side port 58 into the enlarged cylinder 40, and through its discharge or exhaust ports 41a into the bore hole surrounding the apparatus. At this time, compressed air can pass from the inlet ports 28 into the annular groove 56, and then into the hammer return passage 55 to its lower end, acting upon the lower end area of the smaller diameter piston 43 to shift the piston 41 upwardly in the housing and the cylinder sleeve away from the anvil 10. Such air under pressure can also pass through a side port 66 communicating with the return hammer passage 55 into the annular space 66a above the lower cylinder sleeve 19 and below the enlarged piston portion 44, acting on the annular area S of the hammer piston and assisting in shifting the piston to its upper position.

The hammer piston moves only a short distance on its upward or return stroke before the labyrinth seals 60 below its annular groove 56 close the inlet ports 28, the compressed air introduced through the hammer return passage 55 continuing to expand, driving the hammer piston 41 upwardly until its upper end impacts against a lower spring seat 70 engaged by a plurality of spring discs 71, such as Belleville springs, the upper end of which bear against the lower head 32 of the upper tubular member 31, which functions as an upper spring seat. The kinetic energy in the hammer piston 41 is transferred to the springs 71, and also to the air trapped in the chamber 65 above the piston, which it is compressing.

Near the top of the hammer piston stroke, the impact passage side port 58 is placed in communication with the inlet ports 28, the seal ring 61 on the enlarged piston portion 44 sealing against the enlarged cylinder wall 24 above the discharge ports 41a and the labyrinth seals 60 above the side port 58 sealingly engaging the upper cylinder sleeve 25 above the inlet ports 28 (FIG. 2a). As a result, compressed air flows from the annular passage 30 through the ports 28 into the impact passage 57 to the upper end of the piston 41, forcing the piston downwardly, aided by the energy stored in the Belleville springs 71 and the compressed air in the cylinder space 65. Because of the large length and volume of the cylinder space, a large quantity of air under pressure is introduced through the impact passage 57 into the chamber 65, such compressed air shifting the hammerpiston 41 downwardly, the inlet ports 28 being closed off after a relatively short downward movement of the piston, because of the sealing action of the labyrinth seals 60 against the wall of the upper cylinder sleeve 25 below the inlet ports 28.

However, the compressed air above the piston expands and propels the hammer piston 41 downwardly, causing it to impact against the anvil head 45, such impact blow being delivered through the drill bit D to the bottom F of the bore hole. During the downstroke of the hammer piston 41, when the upper seal 61 on the enlarged hammer piston portion 44 moves below the discharge ports 41a, the air above the impact piston can exhaust through the impact passage 57, its side port 58, and the housing discharge ports 41a into the annulus surrounding the housing 11, to convey the cuttings upwardly around the apparatus and through the annulus surrounding the string of drill pipe B to the top of the bore hole.

Immediately prior to the hammer piston impacting against the anvil head 45, the annular piston groove 56 moves into communication with the inlet ports 28, the compressed air passing through the return passage 55 to the bottom of the piston and into the annular space below the enlarged piston portion 44, to return the piston 41 to its upper position. The foregoing cycle is then repeated.

It should be noted that when the hammer piston 41 is at the upper end of its stroke, its lower end is disposed above the upper exhaust ports 21 in the lower cylinder sleeves 19 (FIG. 2a 21)), allowing the compressed air in the lower cylinder sleeve 19 below the piston and in the annular space 66a to pass through the upper exhaust ports 21 into the annular exhaust passage 20, from where the air will flow through the lower ports 22 into the anvil passage 50, 51, and then out through the bit nozzles 52 to clean the bottom F of cuttings and to maintain the drill bit in a clean and cool condition.

The area available over which the compressed air acts on the downstroke or power stroke of the piston is the full cross-sectional area of the small diameter upper piston portion 42 plus the annular area S of the intermediate piston portion 44 between the small diameter piston portion and the wall 24 of the large cylinder 40. In other words, the annular area available for delivery on the power stroke is the full cross-sectional area of the enlarged intermediate piston portion 44, or the area across the inner wall 24 of the larger cylinder. A corresponding area is available for propelling the hammer piston 41 upwardly on its return stroke. The large areas over which compressed air can act is much greater than would be available if the hammer piston were made of a uniform diameter throughout its length, in view of the restrictions imposed within the housing by the upper and lower cylinder sleeves 25, 19. Because of the availability of the much greater piston area on which the compressed air can act, more power is imparted to the piston, such that even when relatively low air pressures only are available, sufficient kinetic energy can be imparted to the piston to cause it to deliver an effective impact blow upon the anvil 10 and the bit D attached thereto. In addition to the larger piston area that is provided in the apparatus, the large volume of the cylinder space or chamber 65 above the piston permits the introduction of more high pressure air into the apparatus for action upon the piston on its downstroke, permitting more power to be developed, since the compressed air does not reduce in pressure to as great an extent during the downstroke of the hammer piston and before the air can exhaust through the ports 41a.

The discharge of the compressed air upon the downstroke of the hammer piston through the discharge ports 41a provides a direct travel path for the air into the bore hole for lifting the cuttings to the top of the hole, such air being provided in a comparatively large volume. Such air need not traverse a circuitous path, as is necessary for the compressed air below the piston 41 to follow at the end of the piston upstroke, which enhances the efficiency of the apparatus. Particularly in air hammers of small size, the direct exhaust of the power air into the annulus surrounding the apparatus insures a sufficient air volume for carrying the the cuttings out of the bore hole. The required volumes of air are difficult to provide in prior air hammers of small diameter. The elimination of the necessity for a large portion of the exhaust air to traverse a tortuous path insures a rapid escape of the power air and, therefore, results in less air being trapped in the cylinder 25 and chamber 65 above the piston upon its upstroke, so that the piston on its upstroke need perform less work in compressing air trapped thereabove.

The apparatus illustrates the Belleville or annular, tapered disc springs in which the energy of the hammer piston 41 is stored on its upstroke, and which returns the energy to the piston on its downstroke, the downward expansion of the stack of disc springs being limited by engagement of its lower seat 70 with an upwardly facing shoulder 70a formed in the upper cylinder sleeve. Apparatus embodying the conical spring arrangement is both described and claimed in the application of Alfred R. Curington, Ser. No. 100,887, filed Dec. 23, 1970, for High Frequency Pneumatically Actuated Drilling Hammer The apparatus is rendered inoperable unless the bit D is resting upon the bottom F of the hole C, with a required amount of drilling weight imposed upon it by the drill pipe B. When the drill pipe is elevated to raise the bit from the bottom of the hole, the anvil 10 and bit D drop downwardly, as permitted by the telescoping of the anvil 10 within the lower sub 18, until an external anvil flange 80 engages a plurality of circumferentially spaced limit pins 81 extending through bores 82 in the lower sub 18 and held in an inward position by a depending skirt 83 of the lower housing section 17. Such lower positioning of the anvil permits the piston to drop downwardly within the upper and lower cylinder sleeves 25, 19 and intermediate larger cylinder 40 to a position determined by engagement of the enlarged piston portion 44 with the upper end of the lower cylinder sleeve 19, at which time the annular groove 56 of the piston still communicates with the inletports 28, the impact head being disposed in an enlarged internal diameter portion 84 of the lower cylinder sleeve, such that compressed air can be pumped through the apparatus and through the hammer return passage 55, discharging from the lower end of the piston and passing around the impact head 45 for continued flow through the ports 50 into the central passage 51 of the anvil and out through the bit nozzles 52, With the parts in this position, compressed air can be pumped continuously through the apparatus to clean the bit D of cuttings and impart a circulating action upwardly through the annulus surrounding the apparatus A and the drill pipe B to the top of the bore hole. It is only when drilling weight is imparted to the drill bit, with the housing structure 11 telescoped downwardly overthe anvil 10, to hold the drill bit D against the bottom F of the bore hole, that the apparatus becomes operative.

ICLAIM:

1. ln percussion drilling apparatus: an outer housing structure connectible to a drill string;.an anvil in the lower portion of said housing structure and connectible to a drill bit; said housing structure including a first cylinder and a second cylinder therebelow of greater internal diameter than the internal diameter of said first cylinder; a hammer piston reciprocable in said cylinders for intermittently impacting against said anvil, said piston having an upper portion slidably reciprocable in said first cylinder and in sealed relation thereto and a lower portion of greater diameter than said upper portion slidably reciprocable in said second cylinder and in sealed relation thereto; said upper portion having an effective cross-sectional area substantially equal to the internal cross-sectional area of said first cylinder; means for directing a fluid medium under pressure into said first cylinder above said upper piston portion for action upon the full effective cross-sectional area of said upper piston portion and into said second cylinder above said lower piston portion for driving said hammer piston downwardly .toward said anvil; and means for directing the fluid medium under pressure into a lower portion of said housing structure for action upon said hammer piston to elevate said hammer piston in said housing structure.

2. In apparatus as defined in claim 1; said structure having discharge ports communicating with the interior of said second cylinder through which fluid medium exhausts directly to the exterior of said structure after downward movement of said hammer piston along said first and second cylinders.

3. In apparatus as defined in claim 1; said second cylinder having discharge ports controlled by said lower piston portion through which fluid medium in said first cylinder above said upper piston portion and fluid medium in said second cylinder exhaust after downward movement of said hammer piston along said first and second cylinders.

4. ln apparatus as defined in claim 1; said hammer piston shifting in said first and second cylinders to alternately control flow of the fluid medium into said lower portion of said housing structure and said first and second cylinders.

5. ln apparatus as defined in claim 1; said hammer piston shifting in said first and second cylinders to alternately control flow of the fluid medium into said first and second cylinders and said lower portion of said housing structure; and means for alternately exhausting the fluid medium from said first and second cylinders and said lower portion of said housing structure.

6. In apparatus as defined in claim 1; said hammer piston shifting in said first and second cylinders to alternatively control flow of the fluid medium into said first and second cylinders and said lower portion of said housing structure; said housing structure having discharge ports communicating with the interior of said second cylinder through which fluid medium exhausts after downward movement of said hammer piston along said first and second cylinders; and means for exhausting the fluid medium from saidlower portion of said housing structure'after upward movement of said hammer piston in said housing structure.

7. In apparatus as defined in claim 1; said hammer piston shifting in said first and second cylinders to alternately control flow of the fluid medium into said lower portion of said housing structure and said first and second cylinders; said second cylinder having discharge ports controlled by said lower piston portion through which fluid medium in said first cylinder above said upper piston portion and fluid medium in said second cylinder exhaust after downward movement of said hammer piston along said first and second cylinders; and means for exhausting the fluid medium from said lower portion of said housing structure after upward movement of said hammer piston in said housing structure.

8. In percussion drilling apparatus: a housing structure connectible to a drill string; an anvil in the lower portion of said housing structure and connectible to a drill bit; said housing structure including an upper cylinder, a lower cylinder, and an intermediate cylinder therebetween of greater internal diameter than the diameters of said upper and lower cylinders; a hammer piston reciprocable in all of said cylinders for intermittently impacting against said anvil, said piston having upper and lower portions slidably reciprocable in said upper and lower cylinders, respectively, in sealed relation thereto to and an intermediate portion of greater diameter than said upper and lower piston portions slidably reciprocable in said intermediate cylinder in sealed relation thereto; said upper piston portion having an effective cross-sectional area substantially equal to the internal cross-sectional area of said upper cylinder; means for directing a fluid medium under pressure into said upper cylinder above said upper piston portion for action upon the full effective crosssectional area of said upper piston portion and into said intermediate cylinder above said intermediate piston portion for driving said hammer piston downwardly toward said anvil, and means for directing the fluid medium under pressure into a lower portion of said housing structure for action upon said hammer piston to elevate said hammer piston in said housing structure.

9. In apparatus as defined in claim 8; said last-mentioned means directing the fluid medium under pressure into said lower cylinder below said lower piston portion.

10. In apparatus as defined in claim 8; said last-mentioned means directing the fluid medium under pressure into said lower cylinder below said lower piston portion and into said intermediate cylinder below said intermediate piston portion.

11. In apparatus as defined in claim 8; said intermediate cylinder having discharge ports controlled by said intermediate piston portion through which fluid medium in said upper cylinder above said upper portion and fluid medium in said intermediate cylinder exhaust after downward movement of said hammer piston along said upper, intermediate and lower cylinders.

12. In apparatus as defined in claim 8; said hammer piston shifting in said cylinders to alternately control flow of the fluid medium into said upper and intermediate cylinders and said lower portion of said housing structure.

13. In apparatus as defined in claim 8; said last-mentioned means directing the fluid medium under pressure into said lower cylinder below said lower piston portion; said hammer piston shifting in said cylinders to alternately control flow of the fluid medium into said upper and intermediate cylinders and lower cylinder.

14. In apparatus as defined in claim 8; said last-mentioned means directing the fluid medium under pressure into said lower cylinder below said lower piston portion; said hammer piston shifting in said cylinders to alternately control flow of the fluid medium into said upper and intermediate cylinders and lower cylinder; said intermediate cylinder having discharge ports controlled by said intermediate piston portion through which fluid medium in said upper cylinder above said upper piston portion and fluid medium in said intermediate cylinder exhaust after downward movement of said hammer piston along said upper, intermediate and lower cylinders; and means controlled by said lower piston portion for exhausting the fluid medium from said lower cylinder after upward movement of said hammer piston in said upper, intermediate and lower cylinders.

15. In percussion drilling apparatus: an outer housing structure connectible to a drill string; an upper cylinder in said housing structure and forming therewith an upper high fluid pressure passage; a lower cylinder in said housing structure spaced longitudinally below said upper cylinder and forming with said structure a lower fluid pressure passage; said housing structure providing an intermediate cylinder between said upper and lower cylinders of a substantially greater internal diameter than the internal diameters of said upper and lower cylinders; an'anvil extending into the lower portion of said lower cylinder to close the same; a hammer piston reciprocable in all of said cylinders for intermittently impacting against said anvil; said upper cylinder having an inlet port through which fluid may flow from said upper passage into said upper cylinder; said lower cylinder having an exhaust port through which fluid may flow from said lower cylinder to said lower passage; said piston including upper and lower small diameter piston portions reciprocable in said upper and lower cylinders, respectively, and an intermediate large diameter piston portion reciprocable in said intermediate cylinder; said intermediate cylinder having discharge ports communicating the interior of said intermediate cylinder with the exterior of the housing structure; said piston having an impact passage communicating with said upper cylinder above said upper piston and intermediate cylinder and its discharge ports when said piston is in a lower position in said cylinders, said impact passage communicating with said upper cylinder above said upper piston and with said upper passage when said piston is in an upper position in said cylinders, at which time said intermediate portion closes said discharge ports; said piston having a return passage communicating with said lower cylinder below said lower piston portion and with said upper passage when said piston is in a lower position in said cylinder; said lower piston portion closing said lower passage when said piston is in a lower position in said cylinders and opening said lower passage to the interior of said lower cylinder when said piston is in an upper position in said cylinders.

16. In apparatus as defined in claim 15; said lower piston portion having a side port establishing fluid communication between said return passage and inter mediate cylinder below said large piston portion.

17. In apparatus as defined in claim and passage means in said anvil communicating with said lower passage to conduct fluid medium to the drill bit.

a e t a 1 

1. In percussion drilling apparatus: an outer housing structure connectible to a drill string; an anvil in the lower portion of said housing structure and connectible to a drill bit; said housing structure including a first cylinder and a second cylinder therebelow of greater internal diameter than the internal diameter of said first cylinder; a hammer piston reciprocable in said cylinders for intermittently impacting against said anvil, said piston having an upper portion slidably reciprocable in said first cylinder and in sealed relation thereto and a lower portion of greater diameter than said upper portion slidably reciprocable in said second cylinder and in sealed relation thereto; said upper portion having an effective cross-sectional area substantially equal to the internal crosssectional area of said first cylinder; means for directing a fluid medium under pressure into said first cylinder above said upper piston portion for action upon the full effective crosssectional area of said upper piston portion and into said second cylinder above said lower piston portion for driving said hammer piston downwardly toward said anvil; and means for directing the fluid medium under pressure into a lower portion of said housing structure for action upon said hammer piston to elevate said hammer piston in said housing structure.
 2. In apparatus as defined in claim 1; said structure having discharge ports communicating with the interior of said second cylinder through which fluid medium exhausts directly to the exterior of said structure after downward movement of said hammer piston along said first and second cylinders.
 3. In apparatus as defined in claim 1; said second cylinder having discharge ports controlled by said lower piston portion through which fluid medium in said first cylinder above said upper piston portion and fluid medium in said second cylinder exhaust after downward movement of said hammer piston along said first and second cylinders.
 4. In apparatus as defined in claim 1; said hammer piston shifting in said first and second cylinders to alternately control flow of the fluid medium into said lower portion of said housing structure and said first and second cylinders.
 5. In apparatus as defined in claim 1; said hammer piston shifting in said first and second cylinders to alternately control flow of the fluid medium into said first and second cylinders and said lower portion of said housing structure; and means for alternately exhausting the fluid medium from said first and second cylinders and said lower portion of said housing structure.
 6. In apparatus as defined in claim 1; said hammer piston shifting in said first and second cylinders to alternatively control flow of the fluid medium into said first and second cylinders and said lower portion of said housing structure; said housing structure having discharge ports communicating with the interior of said second cylinder through which fluid medium exhausts after downward movement of said hammer piston along said first and second cylinders; and means for exhausting the fluid medium from said lower portion of said housing structure after upward movement of said hammer piston in said housing structure.
 7. In apparatus as defined in claim 1; said hammer piston shifting in said first and second cylinders to alternately control flow of the fluid medium into said lower portion of said housing structure and said first and second cylinders; said second cylinder having discharge ports controlled by said lower piston portion through which fluid medium in said first cylinder above said upper piston portion and fluid medium in said second cylinder exhaust after downward movement of said hammer piston along said first and second cylinders; and means for exhausting the fluid medium from said lower portion of said housing structure after upward movement of said hammer piston in said housing structure.
 8. In percussion drilling apparatus: a housing structure connectible to a drill string; an anvil in the lower portion of said housing structure and connectible to a drill bit; said housing structure including an upper cylinder, a lower cylinder, and an intermediate cylinder therebetween of greater internal diameter than the diameters of said upper and lower cylinders; a hammer piston reciprocable in all of said cylinders for intermittently impacting against said anvil, said piston having upper and lower portions slidably reciprocable in said upper and lower cylinders, respectively, in sealed relation thereto to and an intermediate portion of greater diameter than said upper and lower piston portions slidably reciprocable in said intermediate cylinder in sealed relation thereto; said upper piston portion having an effective cross-sectional area substantially equal to the internal cross-sectional area of said upper cylinder; means for directing a fluid medium under pressure into said upper cylinder above said upper piston portion for action upon the full effective cross-sectional area of said upper piston portion and into said intermediate cylinder above said intermediate piston portion for driving said hammer piston downwardly toward said anvil, and means for directing the fluid medium under pressure into a lower portion of said housing structure for action upon said hammer piston to elevate said hammer piston in said housing structure.
 9. In apparatus as defined in claim 8; said last-mentioned means directing the fluid medium under pressure into said lower cylinder below said lower piston portion.
 10. In apparatus as defined in claim 8; said last-mentioned means directing the fluid medium under pressure into said lower cylinder below said lower piston portion and into said intermediate cylinder below said intermediate piston portion.
 11. In apparatus as defined in claim 8; said intermediate cylinder having discharge ports controlled by said intermediate piston portion through which fluid medium in said upper cylinder above said upper portion and fluid medium in said intermediate cylinder Exhaust after downward movement of said hammer piston along said upper, intermediate and lower cylinders.
 12. In apparatus as defined in claim 8; said hammer piston shifting in said cylinders to alternately control flow of the fluid medium into said upper and intermediate cylinders and said lower portion of said housing structure.
 13. In apparatus as defined in claim 8; said last-mentioned means directing the fluid medium under pressure into said lower cylinder below said lower piston portion; said hammer piston shifting in said cylinders to alternately control flow of the fluid medium into said upper and intermediate cylinders and lower cylinder.
 14. In apparatus as defined in claim 8; said last-mentioned means directing the fluid medium under pressure into said lower cylinder below said lower piston portion; said hammer piston shifting in said cylinders to alternately control flow of the fluid medium into said upper and intermediate cylinders and lower cylinder; said intermediate cylinder having discharge ports controlled by said intermediate piston portion through which fluid medium in said upper cylinder above said upper piston portion and fluid medium in said intermediate cylinder exhaust after downward movement of said hammer piston along said upper, intermediate and lower cylinders; and means controlled by said lower piston portion for exhausting the fluid medium from said lower cylinder after upward movement of said hammer piston in said upper, intermediate and lower cylinders.
 15. In percussion drilling apparatus: an outer housing structure connectible to a drill string; an upper cylinder in said housing structure and forming therewith an upper high fluid pressure passage; a lower cylinder in said housing structure spaced longitudinally below said upper cylinder and forming with said structure a lower fluid pressure passage; said housing structure providing an intermediate cylinder between said upper and lower cylinders of a substantially greater internal diameter than the internal diameters of said upper and lower cylinders; an anvil extending into the lower portion of said lower cylinder to close the same; a hammer piston reciprocable in all of said cylinders for intermittently impacting against said anvil; said upper cylinder having an inlet port through which fluid may flow from said upper passage into said upper cylinder; said lower cylinder having an exhaust port through which fluid may flow from said lower cylinder to said lower passage; said piston including upper and lower small diameter piston portions reciprocable in said upper and lower cylinders, respectively, and an intermediate large diameter piston portion reciprocable in said intermediate cylinder; said intermediate cylinder having discharge ports communicating the interior of said intermediate cylinder with the exterior of the housing structure; said piston having an impact passage communicating with said upper cylinder above said upper piston and intermediate cylinder and its discharge ports when said piston is in a lower position in said cylinders, said impact passage communicating with said upper cylinder above said upper piston and with said upper passage when said piston is in an upper position in said cylinders, at which time said intermediate portion closes said discharge ports; said piston having a return passage communicating with said lower cylinder below said lower piston portion and with said upper passage when said piston is in a lower position in said cylinder; said lower piston portion closing said lower passage when said piston is in a lower position in said cylinders and opening said lower passage to the interior of said lower cylinder when said piston is in an upper position in said cylinders.
 16. In apparatus as defined in claim 15; said lower piston portion having a side port establishing fluid communication between said return passage and intermediate cylinder below said large piston portion.
 17. In apparatus as defined in claim 15; and passage means in said aNvil communicating with said lower passage to conduct fluid medium to the drill bit. 